Upon a time a man came to the Orlanthi, or a dragon in the shape of a man. He spoke of friendship and joining into the knowledge of the dragons. Some of the Orlanthi clans joined the dragonkin, others stayed aloof whilst yet again others turned him away.
Those that joined the dragonkin moved to Dragon Pass, and thus was born the Empire of Dragon Friends which lasted until the dragons rose up and ate everyone.
You can read the full story at The Dragonkill War (story).